Methods and apparatus for compensating for propagation delays in coordinated multi-point transmission

Abstract

Systems and techniques for communication using coordinated multi-point transmission. In one embodiment, an apparatus comprises at least one processor and a memory storing a set of computer instructions, configured. The processor is configured to cause the apparatus to determine a linear phase variation between at least first and second transmissions from first and second transmission points based at least in part on a propagation delay difference between the first and second transmissions, and transmit the phase variation information for at least the first and the second transmissions. An apparatus configured to operate as a transmission point in a network receives linear phase variation information indicating phase variation experienced by at least one user equipment resulting from a propagation delay difference between at least the apparatus and a second apparatus operating as a second transmission point and manages transmission so as to control phase variation resulting from the propagation delay difference.

We claim: 
     
       1. An apparatus comprising;
 a processing system comprising at least one processor and a memory storing a set of computer instructions, wherein the processing system is configured to cause the apparatus to at least: 
 compute a linear phase variation based at least in part on a propagation delay difference between at least a first radiofrequency transmission from at least a first transmission point and at least a second radiofrequency transmission from at least a second transmission point; and 
 transmit information indicating the phase variation for at least the first and the second transmissions; 
 
       wherein the first and the second radiofrequency transmissions each comprise a plurality of sub-bands and wherein the processor causes the apparatus to compute the phase variation for each sub-band based at least in part on the propagation delay between the first and the second transmission with respect to each sub-band. 
     
     
       2. The apparatus of  claim 1 , wherein the processing system is configured to cause the apparatus to measure a propagation delay difference between the first and the second transmissions and compute the phase variation based on the measured propagation delay difference. 
     
     
       3. The apparatus of claim wherein the processing system is configured to cause the apparatus to estimate the phase variation in the frequency domain. 
     
     
       4. The apparatus of  claim 1 , wherein the first transmission point is a reference transmission point and wherein the apparatus receives radiofrequency transmissions from each of the second transmission points and a plurality of additional transmission points and computes the phase variation based at least in part on respective propagation delay differences between transmissions from the reference transmission point and each of the second and the additional transmission points. 
     
     
       5. The apparatus of  claim 1 , wherein the memory stores a codebook indexing each of a plurality of codes to a specific phase variation value and wherein transmission of the information indicating the phase variation comprises transmission of it code indexed to the phase variation value. 
     
     
       6. The apparatus of  claim 5 , wherein the codebook comprises codes based on a phase shift keying (PSK) complex alphabet. 
     
     
       7. The apparatus of  claim 6 , wherein the phase shift keying alphabet is selected based at least in part on a quantization error exhibited by a multi-transmission point feedback combiner of at least one of the transmission points. 
     
     
       8. The apparatus of  claim 1  wherein the apparatus is a user equipment conducting communication using orthogonal frequency division multiplexing (OFDM) and wherein the apparatus is operative to receive OFDM transmissions from the transmission points. 
     
     
       9. The apparatus of  claim 1 , wherein the apparatus is configured to provide channel state information feedback in support of coordinated multi-point transmission from multiple transmission points. 
     
     
       10. A method comprising:
 receiving at least a first radiofrequency transmission from a first transmission point and a second radiofrequency transmission from a second transmission point; 
 operating a processor to compute a linear phase variation based at least in part on propagation delay differences between transmissions from at least the first and the second transmission point; and 
 transmitting information indicating the phase variation to at least one of the transmission points; 
 
       wherein the first and the second radiofrequency transmissions each comprise a plurality of sub-bands and wherein the phase variation is computed based at least in part on the propagation delay with respect to corresponding sub-bands of the first and second transmissions and wherein computing a phase variation comprises computing a phase variation for each sub-band. 
     
     
       11. The method of  claim 10 , wherein the first transmission point is a reference transmission point, wherein receiving at least first and second radiofrequency transmissions comprises receiving radiofrequency transmissions from each of the second transmission points and a plurality of additional transmission points, and wherein the phase variation is computed based at least in part on respective propagation delay differences between transmissions from the reference transmission point and each of the second and the additional transmission points. 
     
     
       12. The method of  claim 10 , further comprising storing a codebook indexing each of a plurality of codes to a specific phase variation value and wherein transmission of the information indicating the phase variation comprises transmission of a code indexed to the phase variation value. 
     
     
       13. The method of  claim 12 , wherein the codebook comprises codes based on a phase shift keying (PSK) complex alphabet. 
     
     
       14. The method of  claim 10 , wherein the radiofrequency transmissions are orthogonal frequency division multiplexing (OFDM) transmissions.